1. Field of the Invention
The present invention generally relates to apparatuses (e.g., drives) for optical media such as optical tape and optical discs (e.g., Blu-ray Disc™, DVD), and more particularly to a testing and evaluation device that can write data to and read data from a piece of unformatted optical media.
2. Relevant Background
Optical media (e.g., optical tape, optical discs) are storage media that hold content in digital form and that are written and read by one or more lasers (e.g., embodied in optical pickup units or OPUs). Over time, optical media has become preferred to magnetic media (e.g., floppy disk) because of increased storage ability and durability. For instance, optical media may encode binary data in the form of “pits” (e.g., indentations, indicia), and “lands” (e.g., platforms, grooves) on one or more encoding or recording layers (e.g., each including a dye recording layer, a phase change material such as AgInSbTe, and/or a semi transparent metal reflecting layer). Pits result in a lack of or less (e.g., distorted) reflection when read by a laser and may equate to a binary value or zero “off,” whereas lands reflect laser light and may equate to a binary value of one or “on”. In some arrangements, pits may be disposed or located on the lands or grooves. For instance, a series of “2T” or “3T” patterns may be formed on the optical media.
Generally, the smaller the indicia are on the optical media, the higher the capacity is of the optical media. In any event, the one or more recording layers may be separated by transparent spacers and may be disposed or built up atop a thicker substrate (e.g., polycarbonate) which makes up the bulk of the disc and forms a dust defocusing layer. The other side of the optical disc usually has a printed label, generally made of paper but sometimes printed or stamped onto the disc itself. An optical disc is a flat, usually circular disc while optical tape generally consists of a long and narrow strip of plastic. Patterns and data can be written and read back from such discs and tapes.
In the case of optical discs, one or more continuous, spiral-shaped grooves may typically be formed in or over substantially an entire surface of the polycarbonate layer as part of the manufacturing process and before application of the recording layers, spacers, etc. Optical media having one or more of such grooves formed therein may be referred to as “preformatted” optical media (e.g., a preformatted optical disc). The groove can be defined by a series of sectors, each of which may be associated with particular addressing information that allow an OPU to access a particular track. As used herein, groove, lines and the like typically associated with preformatted optical media will be referred to as “data track location features”. The above-discussed pits and lands (e.g., the encoding pattern) may be formed over or near the groove (e.g., with an OPU) from an innermost track to an outermost track to store data. Forming the pits and lands over the groove allows the data to be accessed by an OPU by way of accessing track addressing information. The data may then be accessed when the data path or pattern is illuminated with a laser diode in an optical disc drive which may spin the disc at speeds of about 200 RPM up to 4000 RPM or more depending on the drive type, disc format, and the distance of the read head from the center of the disc (inner tracks are read at a faster disc speed). In the case of optical tape, grooves and encoding may be associated with helical scan recording, quadruplex recording, or the like.
In any event, testing and evaluation is a vital aspect of the development and production of optical recording and storage media such as tape media, DVD, Blu-ray Disc™, or the like, especially as the size of the pits, lands and other indicia on the optical media decreases. Several methods can be used to assess the quality of optical media such as measuring its optical signals during a process of reading and/or retrieving data (e.g., sum signal, differential push pull tracking error signal, focus error signal), examining the integrity of its physical and logical formats, performing interchange testing, and conducting data verification on the like. For instance, optical signal data may be used to perform a jitter analysis and/or to measure thickness and/or roughness of the media to determine whether the various properties of the optical media are within established tolerances. Each method may be considered a piece of the quality testing puzzle.
Testing and evaluation is typically performed with preformatted optical media (i.e., including grooves stamped or otherwise formed into the media) and a testing device including a single OPU that can both read and write data. That is, after the OPU writes data along one or more grooves or lines of the optical media during the testing process, the same OPU (and/or a laser emanating from the OPU) must be able to return to the grooves or lines where the data was written. For instance, this may mean focusing a lens of the OPU (e.g., via a focusing actuator) or adjusting the entire OPU (e.g., via a sled mechanism). As the testing is performed using preformatted optical media, address information associated with the grooves or lines is accessed to locate and retrieve the written data.